But I looked into it and I think it could really benefit our JK2 community to help organize events like captains, manhunt, tournaments, etc.
I know there's already a "JK Community Discord", but I feel like this is a little bit too off-topic for our JK2 community. (We have special needs and don't care about JKA and other inferior games.)

I know Discord also has it's flaws (proprietary, etc.), but so have the stuff we usually use to stay in contact like fucking Skype and Steam.
I think what benefits us the most is: It runs (almost) everywhere (also in Browser), Voicechat rooms, persistent chat, you don't even have to register to hop in. It could be one place to quickly organize something. Let's try if it works for us!

I've also seen there are ways to link IRC with Discord, so maybe we could look into that too.

For what it's worth, the JK Community group has offered to make JK2 channels and stuff and prefer if we integrate there instead of making our own (hence the name was changed from JKA community to JK community), but I'm almost the only JK2 player on the channel. I'll just follow wherever it happens, I'm on discord anyway for other reasons, and like you said, while it's not perfect, it's a much better option than Skype (*shudder*).